Put a gradebook in percentage mode. Submit a grade for a forum. You submit it as points, but it comes back as a percent. If you resubmit the screen, the percent is now intepreted as points, and you get back a yet large value. The values quickly become very large.
The problem is that gradebookservice setassignmentscore wants points, but msgcenter reads the grade back using getGradesForStudentsForItem. which returns as percent. The code assumes that the units are the same.